The invention relates generally to laser velocimetry and more specifically concerns an instrument, useful in laser velocimetry, for determining coincidence and elapse time between independent sources of random sequential events.
A laser velocimeter, when used in wind tunnel applications, can generate large amounts of data arriving randomly at a high average rate. Advanced measurement concepts, such as vectorial flow field analysis, and turbulence power-spectral-density studies, cannot be undertaken unless additional instrumentation is used. Current methods of processing laser velocimeter data determine the velocity statistics of an independent component of the flow field. These methods do not assure the researcher that each data point is based upon multicomponent measurements of each seeding particle. However, known, coincident, multicomponent measurements of each seeding particle would permit the statistical analysis of the flow velocity vectorial quantities of magnitude and angle. The measurement of power spectral density requires time dependent data; therefore, the time interval between successive measured events must be known. In practice, the autocovariance function is determined by using the velocity data along with the interarrival time data in a Fourier transform to obtain the power spectral density.
Previous methods for determining coincidence used a data validation signal from each flow component electronic instrumentation. The coincidence test would often fail due to the different data dependent processing delays of the instrumentation, even though the flow component measurements were made from the same seeding particle. A coincidence window (aperture), as used in the present invention, permits the adjustment of the coincidence condition to allow for the difference in the processing delays. Although, it is not known whether a current measurement is of interest until coincidence is determined, the interval timing of the measurement events in any one flow component must be accurately maintained.
It is an object of this invention to provide an instrument for determining coincidence of pulses in a first source of pulses with pulses in one or more additional sources of pulses and for determining the time intervals between coincidences.
Another object of this invention is to provide an instrument for determining coincidence of pulses in a first source of pulses with pulses in one or more additional sources of pulses and for determining the time interval between the pulses in the first source in which coincidence occurred.
A further object of this invention is to provide an instrument for determining coincidence of pulses in a first source of pulses with pulses in one or more additional sources of pulses in which the interval of coincidence begins at the leading edges of the pulses in the first source of pulses and end at a predetermined time later (coincidence aperture).
Other objects and advantage of this invention will become apparent hereinafter in the specification and drawings.